No Power - Strange MAF Fault

Stomper

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Hi all looking for some advice re my ML430 (year 2000, 108K miles) loosing power.
For a while all well if I kept the revs below 4000 but if revved any higher than that would start missing terribly and would loose most of its power. Only option then was to stop and switch off/back on. Had a star check done at my local indie which pointed at the MAF being faulty. They had a spare MAF on the shelf but it was for a V6 not the V8 but this fitted as a test and running much better and able to rev as it should. They then ordered me a new MAF but upon fitting running terribly again lacking any power and missing. Suspected new unit faulty so second MAF ordered. In meantime running o.k. with V6 MAF fitted. Second duly arrived but again when fitted running terribly with no power. The indie kindly let me keep the V6 MAF until I could arrange to put the car back in for further checks as I was taking the car to France that weekend. In the meantime seems to be getting worse with the problem of unable to rev above 4000 back. Am going to arrange for car to go back in with them for full checkout but any advice would be greatly appreciated as spoiling my enjoyment of a great car.
p.s. fault same if running on petrol or l.p.g.
 

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Could this be a leak in the air charge pipe or split
 
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Stomper

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First off thanks for the quick reply :).
By air charge pipe I take it you mean the pipe from the air filter to the engine via the MAF? Had a quick look at this but nothing found. I think I need to disconnect it and check it properly. Will do that and report back any findings.
Thanks Dave.
 

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I was wrong as I was thinking of a compressor and you do not have one
 

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Why not try it with the MAF unplugged many go well
 
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Tried it before messing around with the several new MAFs but no change (should have put that in my original post). Think it needs a diagnostic running as I'm driving to see if anything shows up.
 
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television

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Tried it before messing around with the several new MAFs but no change (should have put that iin my original post). Think it needs a diagnostic running as I'm driving to see if anything shows up.

Looks like it is going that way possible a faulty O2 sensor
 

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another possibility is the self adaptation, has it been driven for several journeys with the correct maf? was the boot strapping done when the maf was changed?

obviously you really need diagnosis done with a star machine and suitably experienced technician. were the 113 mafs genuine mercedes?
 

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I never wear boots:confused:;)
 
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MAFs fitted were Bosch units. Not sure if 'boot strapping' done though was connected to a STAR at one point (though not each time it was changed) but not sure what was done while connected. As far as adaption - only did short test drives with both new (V8) MAFs fitted as afraid if I went too far then I wouldn't make it back to the garage it lacking so much power and the ML430 would be a heavy beast to push back LOL.
Could you please tell me would a fried O2 sensor or a blocked cat show up on STAR or is there another way to test them?
 

Alex Crow

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the o2 sensor would show up very easily.

the blocked cat would be harder to pin point with the star machine, but you said it was ok with the 112 maf sensor, this suggests the cats are not blocked.
 
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I never actually saw the results of the STAR just what the mech told me was wrong. When I take it back in I think I will have to ask for the results printout to see if any other faults also showing.
 
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One thing I have noticed is that the air injection pump (at least that’s what I think it is - Merc No.A000 140 37 85 --- Bosch No.0 580 000 011) at the top/front of the engine has gone noisy.
Do you learned ones think that a fault with this could cause the symptoms that I've been experiencing?
 

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That pump only cuts in during certain condition to keep the gasses under control
 

Alex Crow

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as malcolm says.

the pump is to add oxygen to the rich exhaust gas on start up/cold running. this greatly speeds up the cat heating, and lowers co and nox emissions for emission legislation requirements.

not a likely culprit, but a common failure. some sound like they are going to take off :D.
 
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